Calculation to determine the condition the aggregates for concrete mixtures come in

For concrete mixes, fine and coarse aggregates are considered to be in a saturated, surface dry (SSD) condition at the time of introduction into the mix. If the aggregates are not in this condition, then the amount of water required in the mix design must be adjusted, based on the absorption of the aggregate and its moisture content at the time of mixing. Another reason for determining the moisture content of aggregates, particularly fine aggregate, is that when water is present in certain proportions, a phenomenon known as bulking can occur. The volume increases considerably over that in a dry or saturated state because the particles are separated by a film of water.

The total moisture content is found as follows:

((Ww - Wd) ÷ Wd) x 100 = Moisture content

For typical siliceous fine aggregates, absorption can be assumed to be 1%. The free moisture, which appears on the surface of the particles, is therefore found by subtracting 1 from the previous moisture content result. In other words,

((Ww - Wd) ÷ (Wd) x 100) -1 = Free moisture content

Learning exercise

If a 500g (Ww) sample has a constant mass of 478g (Wd) after drying, the weight loss has been from 500 to 478 = 22g, the percentage of free moisture is then:

((500 - 478) ÷ (478) x 100) - 1 = 3.6 %